Method of transferring a substantially disc-shaped workpiece, and device for carrying out this method

ABSTRACT

A method is described for transferring a disc-shaped workpiece from a workpiece carrier, on which the workpiece is fastened along its first main surface by means of a first double-sided adhesive foil, onto a carrier foil, wherein the first double-sided adhesive foil is connected by a first adhesive layer to the workpiece carrier and by a second adhesive layer to the workpiece, with the following process steps: weakening the second adhesive layer through decomposition of its adhesive material down to a reduced adhesive force which is substantially smaller than the adhesive force of the first adhesive layer, fastening the workpiece carrier to a first retaining device, fastening the workpiece with its second main surface to a second retaining device by means of a second double-sided adhesive foil, such that the second double-sided adhesive foil is connected by a third adhesive layer to the second retaining device and by a fourth adhesive layer to the workpiece, and the adhesive forces of the third and the fourth adhesive layer are substantially greater than the adhesive force of the weakened second adhesive layer, separating the workpiece from the first double-sided adhesive foil along the weakened second adhesive layer through the application of a pulling force between the first and the second retaining device, positioning the workpiece with the second retaining device above the carrier foil, weakening the fourth adhesive layer through decomposition of the adhesive substance down to an adhesive force which is substantially smaller than the adhesive force of the third adhesive layer, placing the workpiece on the carrier foil, and separating the workpiece from the second double-sided adhesive foil along the weakened fourth adhesive layer by means of a gas pressure applied between the second double-sided adhesive foil and the workpiece. A device for carrying out this method is also described. A simple and inexpensive removal of a workpiece of the kind mentioned from a workpiece carrier is rendered possible thereby.

The invention relates to a method of transferring a substantiallydisc-shaped workpiece. The invention further relates to a device forcarrying out this method.

A temporary gluing on so-termed workpiece carriers, in particularcarrier discs or carrier plates, is a suitable procedure in the case ofone-sided or two-sided surface treatments of substantially planar, inparticular very thin and brittle workpieces while this treatment isbeing carried out so as to avoid a deformation of the workpieces orindeed fracture thereof. A very thin workpiece in the present contextshould be understood to be a workpiece whose thickness is small inrelation to its length, width, or diameter.

The German patent document 198 50 873 laid open to public inspectiondiscloses a method of processing a substantially disc-shapedsemiconductor technology product which comprises a plurality ofelectronic circuit bodies along at least a first main surface as well asa second main surface situated opposite the first main surface. In thismethod of carrying out treatment processes on one of the main surfacesof the product, a layer-type adhesive material is planarly provided onthe opposite main surface of the product, onto which material adimensionally at least substantially stable carrier element is providedso as to form a planar connection to said opposite main surface of theproduct.

The invention has for its object to provide a method by which a simpleand inexpensive removal of a workpiece of the kind mentioned above froma workpiece carrier is made possible. The invention further has theobject of providing a device for carrying out such a method.

According to the invention, this object is achieved by means of a methodof transferring a substantially disc-shaped workpiece from a workpiececarrier, on which the workpiece is fastened along a first one of itsmain surfaces by means of a double-sided adhesive foil in an at leastsubstantially planar manner, onto a carrier foil on whose surface theworkpiece is to be provided and fastened along said first main surfacein an at least substantially planar manner, which first double-sidedadhesive foil is adhesively connected by a first adhesive layer providedon its first surface to a first surface of the workpiece carrier and bya second adhesive layer provided on its second surface to the workpiecealong the first main surface thereof. The method according to theinvention for this purpose comprises the following process steps:

-   -   weakening the second adhesive layer by an at least partial        decomposition of the adhesive substance forming said second        adhesive layer to a reduced adhesive force which is        substantially smaller than the adhesive force of the first        adhesive layer,    -   fastening the workpiece carrier to a first retaining device,    -   fastening the workpiece along its second main surface opposite        to the first main surface to a surface of a second retaining        device by means of a second double-sided adhesive foil in an at        least substantially planar manner, such that the second        double-sided adhesive foil is adhesively connected by a third        adhesive layer provided on its first surface to the surface of        the second retaining device and by a fourth adhesive layer        provided on its second surface to the workpiece along the second        main surface thereof, and the adhesive forces of the third and        the fourth adhesive layer are substantially greater than the        adhesive force of the weakened second adhesive layer,    -   separating the workpiece from the first double-sided adhesive        foil along the weakened second adhesive layer through the        application of a pulling force between the first and the second        retaining device, which force is at least partly perpendicular        to the main surfaces of the workpiece    -   positioning the workpiece adhesively connected to the second        retaining device and the carrier foil with respect to one        another such that the first main surface of the workpiece faces        the surface of the carrier foil,    -   weakening the fourth adhesive layer through an at least partial        decomposition of the adhesive substance by which it is formed to        a reduced adhesive force which is substantially smaller than the        adhesive force of the third adhesive layer,    -   placing the workpiece with its first main surface on the surface        of the carrier foil in an at least substantially planar manner,        and    -   separating the workpiece from the second double-sided adhesive        foil along the weakened fourth adhesive layer through the        application of a force, generated by gas pressure, between the        second double-sided adhesive foil adhering to the second        retaining device and the workpiece.

The method according to the invention renders it possible in aninexpensive and simple manner to transfer also mechanically vulnerableworkpieces safely from a workpiece carrier onto a carrier foil.

In particular, at least substantially rigidly constructed workpiececarriers can be used for this. The fastening of the workpiece carrier tothe first retaining device may be effected, as desired, by gluing or bymagnetic force.

The adhesive layers which are to be weakened for the transfer maypreferably be prepared with an adhesive substance which is sensitive toheat or to ultraviolet radiation. Weakening of the adhesive layers willthen take place through the influence of heat or ultraviolet radiation.

Further embodiments and particulars of the method according to theinvention are defined in the dependent claims following the main claim1.

For carrying out the method according to the invention, furthermore, adevice is proposed for transferring a substantially disc-shapedworkpiece from a workpiece carrier, on which the workpiece is fastenedalong a first of its main surfaces by means of a first double-sidedadhesive foil in an at least substantially planar manner, onto a carrierfoil on whose surface the workpiece is to be provided and fastened alongsaid first main surface in an at least substantially planar manner. Thefirst double-sided adhesive foil is adhesively connected by a firstadhesive layer provided on its first surface to a first surface of theworkpiece carrier and by a second adhesive layer provided on its secondsurface to the workpiece along the first main surface thereof. Thedevice according to the invention further comprises a first retainingdevice for fastening the workpiece carrier to said first retainingdevice, a second retaining device with a surface on which the workpieceis to be fastened along its second main surface opposite to the firstmain surface by means of a second double-sided adhesive foil in an atleast substantially planar manner, such that the second double-sidedadhesive foil is adhesively connected by a third adhesive layer providedon its first surface to the surface of the second retaining device andby a fourth adhesive layer provided on its second surface to theworkpiece along the second main surface thereof, and the adhesive forcesof the third and the fourth adhesive layer are substantially greaterthan the adhesive force of the second adhesive layer in its weakenedstate.

The device according to the invention further comprises a pulling devicefor separating the workpiece from the first double-sided adhesive foilalong the weakened second adhesive layer through the application of apulling force which is at least partly perpendicular to the mainsurfaces of the workpiece between the first and the second retainingdevice, a device for acting on the second and the fourth adhesive layerfor weakening said adhesive layers through an at least partialdecomposition of the adhesive substance by which they are formed to areduced adhesive force, as well as a gas pressure device for separatingthe workpiece from the second double-sided adhesive foil along theweakened fourth adhesive layer through the application of a force,generated by gas pressure, between the second double-sided adhesive foiladhering to the second retaining device and the workpiece.

The device according to the invention is of a simple construction andrenders possible a reliable, inexpensive, and thus rational manufacture.

Preferably, the device according to the invention is constructed with amagnet device which can be energized or de-energized, as desired, forfastening the workpiece carrier to the first retaining device, theworkpiece carrier being constructed from a ferromagnetic material. Thisrenders possible a simple, fast, and reliable fastening of the workpiececarrier to the first retaining device. If so desired, the workpiececarrier is fastened to the first retaining device by means of gluing.

To enhance the effectiveness of the gas pressure device, a sealingdevice may be provided for forming a substantially gastight seal betweenthe second retaining device and the carrier foil.

Further particulars and embodiments of the device according to theinvention can be found in the dependent claims subsequent to the mainpatent claim 8.

An embodiment of the invention is shown in the drawing and will bedescribed in more detail below. In the drawing:

FIG. 1 shows an example of a workpiece fastened to a workpiece carrierby means of a first double-sided adhesive foil in a diagrammaticrepresentation,

FIG. 2 diagrammatically shows the action of heat or ultravioletradiation for weakening the second adhesive layer between the firstdouble-sided adhesive foil and the workpiece,

FIG. 3 shows the workpiece carrier with the workpiece of FIGS. 1 and 2after fastening to a first retaining device,

FIG. 4 shows the arrangement of FIG. 3 after the workpiece has beenadditionally fastened to a second retaining device,

FIG. 5 is an exploded view of the arrangement of FIG. 4,

FIG. 6 shows the arrangement of FIG. 4 after separation of the workpiecefrom the workpiece carrier,

FIG. 7 shows the second retaining device with the workpiece positionedabove a carrier foil,

FIG. 8 shows the weakening of the adhesive layer by means of which theworkpiece is fastened to the second retaining device,

FIG. 9 shows the placing of the workpiece on the carrier foil,

FIG. 10 shows the separation of the workpiece from the second retainingdevice, and

FIG. 11 shows a modified embodiment of the device shown in FIGS. 3 to 10with a sealing device between the second retaining device and thecarrier foil.

In the diagrammatic drawing of FIG. 1, a workpiece 1, in particular athin semiconductor wafer, is fastened by its first main surface, whichforms the lower side in the position of the workpiece 1 shown here, to aworkpiece carrier 2 by means of a double-sided adhesive foil 3 in aplanar manner. The first double-sided adhesive foil 3 is formed in aknown manner by a foil-type synthetic resin body whose two surfaces arecoated with adhesive layers. A first of these surfaces faces theworkpiece carrier 2 with a first adhesive layer, and a second of thesurfaces faces the workpiece 1 with a second adhesive layer. Thisarrangement is shown in FIG. 5.

FIG. 2 diagrammatically shows the configuration of FIG. 1 with heat orultraviolet radiation acting thereon, indicated by the reference numeral4. This action decomposes the second adhesive layer of the firstdouble-sided adhesive foil 3 at least partly, thus weakening it, so thatits adhesive force is reduced. For this purpose, the second adhesivelayer, unlike the first adhesive layer, of the first double-sidedadhesive foil 3 is made from a heat-sensitive or UV-sensitive material.

FIG. 3 diagrammatically shows the next process step in the embodiment.The workpiece carrier 2 and the workpiece 1 fastened thereon by means ofthe first double-sided adhesive foil 3 are fastened on a first retainingdevice 5 after the second adhesive layer has been weakened. Thisfastening may also be effected through adhesion, or alternatively bymeans of a magnet device which is incorporated in the first retainingdevice and which exerts a magnetic force on the workpiece carrier 2. Theworkpiece carrier 2 will for this purpose be made from a ferromagneticmaterial. The adhesive force of the first adhesive layer between thefirst double-sided adhesive foil 3 and the workpiece carrier 2 as wellas the adhesive force between the workpiece carrier 2 and the firstretaining device 5 are substantially greater here than the adhesiveforce of the weakened second adhesive layer of the first double-sidedadhesive foil 3 by means of which the latter still holds on to theworkpiece 1 in the process step shown here.

As is apparent from FIG. 3, the workpiece carrier 2 is preferably laidwith its entire surface on the first retaining device 5.

FIG. 4 diagrammatically shows the arrangement of the preceding Figuresafter fastening of a second retaining device 6 by means of a seconddouble-sided adhesive foil 7 over a second main surface of the workpiece1 in a planar manner. This second main surface of the workpiece 1 is theupper side thereof in the representation of FIG. 4.

Details of the arrangement shown in FIG. 4 are shown in the explodedview of FIG. 5. This shows diagrammatically from top to bottom in thatorder: the second retaining device 6, the second double-sided adhesivefoil 7, the workpiece 1, the first double-sided adhesive foil 3, theworkpiece carrier 2, an adhesive 8 for fastening the workpiece carrier 2to the first retaining device 5, and this first retaining device 5itself. The second double-sided adhesive foil 7 here carries a thirdadhesive layer on its first surface 9 and a fourth adhesive layer on itssecond surface 11. The first main surface of the workpiece 1 isreferenced 13. The second main surface of the workpiece 1 is referenced14. The first double-sided adhesive foil 3 has the first adhesive layer16 on its first surface 15 and the second adhesive layer 18 on itssecond surface 17. The first surface of the workpiece carrier 2, onwhich the workpiece is fastened by means of the first double-sidedadhesive foil 3, is referenced 19, while a second surface 20 of theworkpiece carrier 2 opposite to said surface 19 serves to fasten saidcarrier to the first retaining device 5.

The next process step in the embodiment shown is depicteddiagrammatically in FIG. 6. Herein, the arrangement of FIG. 4 or 5 isintroduced into a pulling device (not shown), and a pulling force isexerted thereby on the second retaining device 6, indicated with anarrow referenced 21. Since the adhesive forces of all adhesive elementsor layers in the embodiment shown are substantially greater than theadhesive force of the second adhesive layer 18, the application of thepulling force 21 will separate the arrangement of FIG. 4 along saidsecond adhesive layer such that the workpiece 1 detaches itself by itsfirst main surface 13 from the second adhesive layer 18. This situationis shown in FIG. 6.

In the next process step, the first retaining device 5 is removedcomplete with the workpiece carrier 2 still fastened thereon, and thesecond retaining device 6 is positioned with the workpiece above acarrier foil 22. The carrier foil 22 is supported by a planar basesurface 23 for stabilization in the embodiment shown. The situation thusachieved is shown in FIG. 7.

FIG. 8 shows the subsequent process step in which the seconddouble-sided adhesive foil 7 is exposed to heat or ultravioletradiation, again referenced 4 here. The fourth adhesive layer 12 on thesecond surface 11 of the second double-sided adhesive foil 7, by meansof which the workpiece 1 adheres to this second double-sided adhesivefoil 7, is prepared with an adhesive substance which is sensitive toheat or ultraviolet radiation and which can be decomposed through theaction thereof. As a result, the fourth adhesive layer 12 has itsadhesive force reduced to well below the adhesive force obtainingbetween the second double-sided adhesive foil 7 and the second retainingdevice 6 in the process step shown in FIG. 8. The weakening of thefourth adhesive layer 12 takes place before the workpiece 1 is placed onthe carrier foil 22 so as to avoid damage to the carrier foil 22.

In the next process step shown in FIG. 9, the workpiece 1 is provided onthe carrier foil 22, for which purpose the second retaining device 6complete with the workpiece 1 is lowered onto the carrier foil 22 in amovement indicated with the arrow 24. This process step is subject tothe condition that any temperature rise of the workpiece 1 caused by thepreceding process step has first been eliminated.

FIG. 10 diagrammatically shows the next process step of separating theworkpiece 1 from the second double-sided adhesive foil 7 along theweakened fourth adhesive layer 12, again with reference to thearrangement shown in the preceding Figures. The second retaining device6 for this purpose comprises an inner space 25 to which a gas underpressure, preferably compressed air, can be applied through a pressureinlet valve 28. Bores 26 are provided in the portion of the secondretaining device 6 forming the surface 27, on which the workpiece 1 wasfastened by means of the second double-sided adhesive foil 7, throughwhich bores the compressed gas flowing through the inlet 28 can flow outagain. Matching holes are provided in the second double-sided adhesivefoil 7, so that the bores 26 are not covered by the second double-sidedadhesive foil 7. This renders it possible for the gas pressure in theinner space 25 of the second retaining device 6 to act directly on theworkpiece 1, and the second double-sided adhesive foil 7 does not detachitself from the surface 27 of the second retaining device 6. It isensured thereby that the workpiece 1 is separated from the seconddouble-sided adhesive foil 7 and is deposited on the carrier foil 22.

This depositing step is preferably supported in that a movement betweenthe second retaining device 6 and the second double-sided adhesive foil7 connected thereto on the one hand and the carrier foil 22 with thework piece 1 adhered thereto on the other hand is carried out during theseparation of the workpiece 1 from the second double-sided adhesive foil7 at least substantially simultaneously with the application of theforce generated by the gas pressure. This movement is effected so as tobe at least in part perpendicular to the main surfaces of the workpiece1 and is indicated in FIG. 10 by the arrows referenced 30. This movement30 removes the second retaining device 6 from the carrier foil 22 andthe workpiece 1. The simultaneous issuing of gas under pressure throughthe bores 26 is diagrammatically indicated with the arrows 29 in FIG.10.

After the process step described above has been completed, the workpiece1 is present on the carrier foil 22 for further processing, which maytake place at its second main surface 14, said carrier foil beingpreferably constructed as a sawing foil for the case in which theworkpiece 1 is a semiconductor technology product.

FIG. 11 shows a modification of the device described above whichcomprises a sealing device 31 for forming a substantially gastight sealbetween the second retaining device 6 and the carrier foil 22. When agas pressure is provided through the pressure gas inlet valve 28, thepressure on the workpiece 1 can be increased for pressing the latteronto the carrier foil 22 because an overpressure 32 will be built up inthe intermediate space between the second retaining device 6 and thecarrier foil 22. The device shown in FIG. 11 further comprises bores 33in the base support 23 for the carrier foil 22 for providing a vacuumsuction of the carrier foil 22 and the workpiece 1 against the basesurface 23.

In a modified embodiment which is not shown, the workpiece carrier 2 maybe constructed from a ferromagnetic material, and the fastening of theworkpiece carrier 2 to the first retaining device 5 may be effected by amagnet device. The adhesive 8 will be absent in such an embodiment.Furthermore, such a workpiece carrier 2 formed from a ferromagneticmaterial may obviously also be fastened to a first retaining device 5 ofthe kind shown in the embodiment by means of the adhesive 8.

1. A method of transferring a substantially disc-shaped workpiece from aworkpiece carrier, on which the workpiece is fastened along a first oneof its main surfaces by means of a double-sided adhesive foil in an atleast substantially planar manner, onto a carrier foil on whose surfacethe workpiece is to be provided and fastened along said first mainsurface in an at least substantially planar manner, which firstdouble-sided adhesive foil is adhesively connected by a first adhesivelayer provided on its first surface to a first surface of the workpiececarrier and by a second adhesive layer provided on its second surface tothe workpiece along the first main surface thereof, comprising thefollowing process steps: weakening the second adhesive layer by an atleast partial decomposition of the adhesive substance forming saidsecond adhesive layer to a reduced adhesive force which is substantiallysmaller than the adhesive force of the first adhesive layer, fasteningthe workpiece carrier to a first retaining device, fastening theworkpiece along its second main surface opposite to the first mainsurface to a surface of a second retaining device by means of a seconddouble-sided adhesive foil in an at least substantially planar manner,such that the second double-sided adhesive foil is adhesively connectedby a third adhesive layer provided on its first surface to the surfaceof the second retaining device and by a fourth adhesive layer providedon its second surface to the workpiece along the second main surfacethereof, and the adhesive forces of the third and the fourth adhesivelayer are substantially greater than the adhesive force of the weakenedsecond adhesive layer, separating the workpiece from the firstdouble-sided adhesive foil along the weakened second adhesive layerthrough the application of a pulling force between the first and thesecond retaining device, which force is at least partly perpendicular tothe main surfaces of the workpiece, positioning the workpiece adhesivelyconnected to the second retaining device and the carrier foil withrespect to one another such that the first main surface of the workpiecefaces the surface of the carrier foil, weakening the fourth adhesivelayer through an at least partial decomposition of the adhesivesubstance by which it is formed to a reduced adhesive force which issubstantially smaller than the adhesive force of the third adhesivelayer, placing the workpiece with its first main surface on the surfaceof the carrier foil in an at least substantially planar manner, andseparating the workpiece from the second double-sided adhesive foilalong the weakened fourth adhesive layer through the application of aforce, generated by gas pressure, between the second double-sidedadhesive foil adhering to the second retaining device and the workpiece.2. A method as recited in claim 1, wherein a movement which is at leastpartly perpendicular to the main surfaces of the workpiece is carriedout between the first retaining device and the workpiece provided on thecarrier foil during the process of separating the workpiece from thesecond double-sided adhesive foil along the weakened fourth adhesivelayer at least substantially simultaneously with the application of theforce, generated by gas pressure, between the second double-sidedadhesive foil adhering to the second retaining device and the workpiece.3. A method as recited in claim 1, wherein an at least substantiallyrigidly constructed workpiece carrier is used as the workpiece carrier.4. A method as recited in claim 1, wherein the fastening of theworkpiece carrier to the first retaining device is effected by adhesion,such that the adhesive force of the adhesion between the workpiececarrier and the first retaining device is substantially greater than theadhesive force of the weakened second adhesive layer.
 5. A method asrecited in claim 1, wherein the workpiece carrier is constructed with aferromagnetic material, and the fastening of the workpiece carrier tothe first retaining device is effected by means of a magnet device, suchthat the magnetic force obtaining between the workpiece carrier and thefirst retaining device is substantially greater than the adhesive forceof the weakened second adhesive layer.
 6. A method as recited in claim1, wherein the adhesive layers are prepared with a heat-sensitiveadhesive substance, and the weakening of the adhesive layers is achievedthrough the influence of heat.
 7. A method as recited in claim 1,wherein the adhesive layers are prepared with an adhesive substancewhich is sensitive to UV radiation, and the weakening of the adhesivelayers is achieved through the influence of UV radiation. 8-14.(canceled)